1. Field of the Invention
The invention relates to a device for transmitting rotational power from a rotational power source such as an automobile engine to a rotational driven device such as a refrigerant compressor for an air conditioner. The device can rotationally separate the driven device from the rotational power source when the torque transmitted exceeds a predetermined value, that is, the device functions as a torque limiter.
2. Description of the Related Art
Japanese Examined Utility Model Publication (Kokoku) No. 6-14104 describes a rotational power transmission device which has a torque limiting function. The device comprises a drive member which is connected to the crank shaft of an automobile engine through a belt, a driven member which is connected to a shaft of a compressor, and a connecting mechanism between the drive and driven members, which mechanism is provided with levers of rigid material and a spring which is made of a metallic material, in the form of a ring, which engages the levers. The drive member is rotationally connected to the driven member by the engagement between the levers and the spring.
When the drive shaft of the compressor is locked by a failure such as seizing in the compressor and the torque on the connecting mechanism exceeds a predetermined level, the drive levers apply a force on the spring to deform the spring. The deformation of the spring disconnects the engagement between the levers and the spring.
The prior art rotational power transmission device, however, cannot absorb a fluctuation in the torque applied to the device since a metallic spring is used to connect the drive member to the driven member. Therefore, in order to absorb a fluctuation in torque, an additional device must be provided, which increases the production cost.
Further, in an automobile, a driven device, such as a compressor is generally driven by a rotational power transmitted from a crank pulley of the automobile engine through a belt. Therefore, in order to protect the belt from damage, it is desired to have a relatively low shut off torque, for example, 60 Nm, at which the rotational power transmitting device disconnects or disengages.